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How large is the input impedance in the uPD784031?

Latest Updated:12/01/2011

Question:

In the uPD784031, when using a type 20-A pin in the data sheet as an A/D pin, how large is the input impedance?

Answer:

The impedance of this pin changes over time.
Moreover, the sampling capacitor's capacitance is in the order of a few pF.
During sampling, a current flows in order to charge the capacitor, but normally it is just leakage current.
Therefore, the impedance fluctuates according to the status.

This A/D pin must be driven using a low impedance in the order of just a few kΩ.
This is because, during sampling, the sampling capacitor for conversion must be charged within the A/D accuracy.
A high accuracy cannot be obtained when the drive impedance is high.

Suitable Products
RL78 Family
78K0/Dx
78K0/Fx
78K0/Ix
78K0/Kx
78K0/Lx
UPD78F07xx
UPD7800xx
UPD7802xx
UPD7803xx
UPD7807xx
UPD7808xx
UPD7809xx
UPD780xx
UPD78F8025
UPD78403x
78K0/VAN ASCP